An agricultural baler is a trailed machine (PTM—pulled type machine) used in agriculture for the purpose of creating bales of (typically) straw or other biomass such as hay, silage or similar crop material produced during a harvesting or mowing operation.
Various designs of balers have been proposed in the prior art. A common characteristic of virtually all balers is that they are towed behind agricultural vehicles such as tractors. A baler includes an infeed via which biomass is ingested into the interior of the baler where it is compressed or otherwise treated to form bales. The completed bales are tied with twine or another lineal object to make them rigid and self-supporting, after which they are ejected via a discharge chute typically at the rear of the baler so as to fall or be placed on the ground behind the tractor/baler combination as its moves forwardly along a harvested field.
In the 1970's and 1980's, so-called “round” balers were developed. These produce large cylindrical bales. Although many round balers are still sold annually and many more remain in use, in many areas their popularity has been usurped by “rectangular” or “square” balers. Such balers produce cuboid-shaped bales which have a number of advantages over “round” bales.
As a first advantage, the handling of cuboid-shaped bales is more convenient and is safer. Additionally as a result of the cuboid shapes of the bales it is relatively easy to transport them and stack them for temporary or long term storage in stable structures either in fields or in farmyards. Cuboid-shaped bales can be produced with a high density. When used, cuboid-shaped bales are also easily distributed as they are formed from a number of slices.
A significant advantage of rectangular balers over round balers is that it is possible to adjust the characteristics of a cuboid-shaped bale in some cases while the bale is being formed.
This is important because straw or other baled biomass is an economically valuable crop. Very often the value of baled biomass is assessed on the basis of the weight of each bale produced by the operation of the baler. It can be very important to control the density of the baled biomass in order to assure that the bale weights are substantially constant during passage of a baler from one part of a field to another. Variations, however, in the characteristics (especially the moisture) of the baled biomass ingested from different places of the field into the baler may mean that there is a frequent or even constant need to adjust bale density during baling operations in order to meet the objective of constant bale mass.
In a rectangular baler it is possible to adjust the bale density, as the baler includes a substantially cuboid-shaped bale-forming chamber. It is known in the art to construct the bale-forming chamber with one or more moveable side walls. The positions of the side walls can be adjusted so as to alter the volume of the bale-forming chamber and thereby squeeze the bale during its formation to a greater or lesser degree. If, as is commonplace in a baler, each charge or flake of ingested biomass is substantially of constant volume, causing a reduction in the volume of the bale-forming chamber in this way leads to the creation of higher density bales, and vice versa. This, in turn, provides an ability to control the densities of the formed bales.
In more detail, each charge introduced into the bale-forming chamber is, at the point of introduction, uncompressed or compressed to a relatively low level only. It is moved along the bale-forming chamber by longitudinal strokes of a piston or plunger that reciprocates under the action of an attached arm that in turn is driven by a bell crank e.g. secured to a rotating member. Each stroke of the piston therefore compresses an amount of biomass against the biomass already available in the bale-forming chamber. In consequence, the density of the formed bale increases if the volume into which the biomass is swept is reduced as a result of adjustments of the positions of the sidewalls of the chamber at locations “downstream” of the furthest point reached by the piston during its motion.
The dimensions of cuboid-shaped bales, however, are substantially fixed, firstly because of the cross-sectional dimensions of the bale-forming chamber and secondly because the baler forms the biomass into identical bale lengths which are ejected via the discharge as substantially identical, individual bales.
An example of a bale-forming chamber with adjustable sidewall is shown in U.S. Pat. No. 4,037,528. This disclosure describes sidewalls that are moveable under the influence of cam-like arms that are caused to rotate by attached hydraulic rams. The arrangement defines a pair of four-bar linkages each including one of the sidewalls. Operation of the associated ram therefore causes the sidewall to move inwardly or outwardly, relative to the interior of the bale-forming chamber, in an even fashion causing uniform alteration of the chamber volume over a portion of its length. A more modern form of bale density adjustment that is suitable for inclusion in a rectangular baler is disclosed in EP0655190.
In WO2010/100068 the need is disclosed for an approach to apply tension to a bale in a bale chamber of an agricultural baler to enable control of the bale characteristics (in particular the length of bales, especially for small cuboid-shaped bales to facilitate efficiency of use of bale handling equipment) in a consistent way. As described therein the thickness and density of the bale are directly influenced by the amount of crop material delivered to the plunger for each stroke thereof and the resistance applied to the bale being formed in the chamber behind the plunger. Resistance applied to the bale in the chamber is commonly controlled by variations in the size of the cross-section of the chamber through which the crop material is being urged by the plunger by adjusting the position of one or more of the chamber side walls to vary the orifice though which the crop material is extruded. In most approaches however the width or height of the chamber is being reduced at a constant rate along the length of the chamber, but this does not result in a constant pressure on the bale, while in improved approaches as in WO2010/100068, two zones are provided wherein the rate of change in cross-sectional area experienced by the bale travelling through the zones is different for those zones. For obtaining this, a bend or pivot is provided in at least one of the side walls, also called chamber doors. Such realization provides an increased resistance against which the plunger may compress the crop material to form the bale in a first zone, while in the second zone just a sufficient pressure on the bale surface is maintained.
It is a disadvantage of balers with a pivot in the side walls that for dry slippery crops as for example harvested in southern France, a big bend is needed to provoke sufficient resistance for baling at high density. This aggressive angle would create, however, too much resistance for longer and less dry crops, such as for example harvested in northern France or England.